A packet transport service described in RFC (Request For Comments) 3985, “Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture”, March 2005 describes a packet transport service that emulates a telecommunications service (e.g., Ethernet, Frame Relay, ATM (Asynchronous Transfer Mode), TDM (Time-division multiplexing), SONET/SDH (Synchronous Optical Networking/Synchronous Digital Hierarchy)) over a PSN (Packet Switched Network) (e.g., an MPLS (Multiprotocol Label Switching) including a MPLS-TP (Transport Profile) PSN). In a general network model, the service is emulated between customer edge network elements that communicate over the PSN through one or more pseudowires provided by provider edge network elements. A network element (e.g., a router, switch, bridge) is a piece of networking equipment, including hardware and software, that communicatively interconnects other equipment on the network (e.g., other network elements, end stations such as subscriber end stations and server end stations). A customer edge network element is a network element where one end of the service originates and/or terminates, and is typically unaware that the service is being emulated. Each customer edge network element is coupled to a provider edge network element through an attachment circuit (AC), which is a physical or virtual circuit (e.g., Frame Relay DLCI (data link connection identifier), ATM VPI/VCI (Virtual Path Identifier/Virtual Circuit Identifier), Ethernet, VLAN (Virtual Local Area Network), etc.). The provider edge network elements are coupled together through one or more pseudowires. A PSN tunnel is established to provide a data path for the pseudowires. The pseudowire traffic is invisible to the core network (e.g., one or more intermediate provider network elements between provider edge network elements). Native data units (e.g., Ethernet frames) are received on the attachment circuits and are encapsulated in pseudowire-protocol data units (PW-PDUs) n to be carried across the PSN via the pseudowires in the PSN tunnel. The provider edge network elements perform the encapsulation and decapsulation of PW-PDUs.
A pseudowire which is able to carry any number and type of protocols is a packet-pseudowire and may have unique control word and other embedded encodings. These protocols may include control protocols (e.g., ARP (Address Resolution Protocol), LLDP (Link Layer Discovery Protocol), etc.) and/or other client protocols such as IP and MPLS. In certain network deployments, client protocols such as IP and MPLS take up the majority of the bandwidth of the service compared to the control protocols.
There have been several different approaches that have been suggested for encapsulation formats for a packet-pseudowire, described in IETF draft “Packet Pseudowire Encapsulation over an MPLS PSN”, draft-bryant-pwe3-packet-pw-03, Mar. 8, 2010 (hereinafter “draft-bryant”). The encapsulation format recommended by draft-bryant proposes a technique using virtual Ethernet to provide a packet-pseudowire and use an Ethernet pseudowire (described in RFC 4448, “Encapsulation Methods for Transport of Ethernet over MPLS Networks”, April 2006) to carry the user traffic. An Ethernet pseudowire carries all the data link layer headers, regardless of whether the underlying protocol is a control protocol or a client protocol such as IP and MPLS.